The invention relates to a method of manufacturing a display tube comprising an envelope having a display window, in which a transparent plate is secured on said display window during a process step, and the envelope is evacuated during another process step.
A method of the type mentioned in the opening paragraph is known from French Patent Specification 768,092. In the method described in said specification, the thickness of the display window is just enough to resist the difference in air pressure during the evacuation of the envelope. The display tube is protected against implosion (i.e., it is made resistant to vibrations and shocks) by bonding a glass plate to the display window by means of an adhesive layer, after the evacuation process.
In practice it has been found, however, that a colour display tube manufactured according to said known method may display images having insufficient colour purity.